1. Field of Invention
This invention relates to valves and, in particular, the field of pneumatic valves.
2. Description of Related Art
It is well known in the field of valves to provide valve control signals for remotely causing valves to open and close, in order to permit fluid flow therethrough. A common method for performing this was to provide a solenoid capable of moving a piston between valve open and valve closed positions. In solenoid controlled valves of this type, a control current was applied to the coil of the solenoid to energize the solenoid and produce electromagnetic flux capable of moving the piston. Many examples of such solenoid actuated valves are known.
One example of a solenoid actuated valve is taught in U.S. Pat. No. 3,379,214, entitled “Permanent Magnet Valve Assembly,” issued to Weinberg on Apr. 23, 1965. Weinberg teaches a permanent magnetic valve assembly, having an electromagnetically actuated valve member, wherein a coil was energized to provide electromagnetic flux. A permanent magnet was also provided to provide permanent magnetic flux. When the flux of the coil that was energized opposed and exceeded the flux of the permanent magnet, a plunger was shifted. A flux in the opposite direction by an opposing current could move the piston in the opposite direction.
U.S. Patent Application Publication No. 2001/0050705, entitled “Magnetically-Actuated Fluid Control Valve”, published on Dec. 13, 2001 and based upon U.S. patent application Ser. No. 09/930,098, also included a magnetic actuator containing both a permanent magnet and an electromagnet. An armature, configured as a see-saw and coupled to the magnetic actuator, caused the valve to open by displacing selected regions of a diaphragm and forcing the diaphragm into contact with a valve seat.
However, solenoid actuated valves can be dangerous in explosive surroundings. For example, they can be dangerous on oil drilling platforms or in use with chemicals in a chemical plant. The danger caused by solenoid valves arises from the fact that the electric current applied to the solenoid coils, for energizing the coils to provide electromagnetic flux to move the pistons under fault conditions can ignite flammable or explosive materials in the vicinity of the valves.
One solution to the problem was to limit the magnitude of the solenoid-actuating current to a level below the level which could possibly ignite a fire or cause an explosion, in a worst case scenario, within the particular hazardous environment where the valve was used. However, limitations on the amount of current that can be used to energize a solenoid places limitations on the size of the piston that can be moved as well as the speed and acceleration of the piston movement. Therefore, it was very difficult and expensive to obtain adequate solenoid activated valves suitable for many applications within hazardous areas.
Another solution was to provide valves that were actuated using permanent magnets rather than solenoids. For example, U.S. Pat. No. 4,942,852, entitled “Electro-Pneumatic Actuator,” issued to Richeson on Jul. 24, 1990, teaches a valve suitable for internal combustion engines. The actuator taught by Richenson was a pneumatically powered transducer for use as a valve mechanism actuator. The transducer had a piston which was powered by a pneumatic source and held in each of its extreme positions. Air control valves were held in their closed positions by pressured air and/or permanent magnet latching arrangements and the control valves are released to supply air to the piston. When the piston was thus released it was driven to the opposing extreme position by the permanent magnetic field. However, even though the Richeson valve used permanent magnet actuation, it was not completely free of electrical circuits.
U.S. Pat. No. 3,517,699, entitled “Magnetic-Pneumatic Proximity Switch,” issued to Marcum on Oct. 20, 1967, teaches a magnetic-pneumatic proximity switch. In the Marcum system, air flow was controlled by a valve without electrical circuit. Instead, a magnetic proximity switch was provided. The magnetic proximity valve taught by Marcum operated as a restriction device in a pneumatic circuit that opened and closed, thereby controlling a spool valve. The spool valve in turn controlled the flow of an operating fluid to or from a working piston and cylinder device.
U.S. Pat. No. 4,630,645, entitled “Pneumatic Switching Device, E.G., For Safeguarding Against Overpressure,” issued to Spa on Dec. 23, 1986, also taught a valve that could be actuated without any electrical current. In the Spa device, a piston was received in a bore of a housing. The piston had a narrowed portion between two end surfaces. Two seals were provided in the narrowed portion that acted cooperatively with seats projecting from the wall of the housing bore towards the piston axis. A compression spring acted on one end face of the piston. The other piston end face delimited a pressure chamber with the housing wherein the air valve was in communication with the pressure chamber. A pilot air aperture had a restriction opening into the chamber and an out flow aperture opened between both housing seats. A signal pressure aperture opened into the bore beyond each seat. The pivotal lever engaged an actuation pin of the air valve.
U.S. Pat. No. 4,964,424, entitled “Pneumatic Valve Assembly For Controlling A Stream of Compressed Air,” issued to Helbig on Oct. 23, 1990. The valve assembly taught by Helbig was adapted for controlling compressed air stream in response to a non-contacting actuation. It included a pivoted one-arm or double-arm lever, a permanent magnet on one side or on each of both sides of its pivotal axis and via a ferromagnetic or magnetic actuating member. The actuating member was moved into proximity of the permanent magnet or magnets by means of a plunger, causing a pilot orifice to be opened or closed. A pilot air stream flowed through the orifice for actuating a pilot piston to move a valve piston to positions in which the valve was opened or closed. Permanent magnets were provided on the lever on both sides of its pivotal axis. The permanent magnets were interconnected by a magnetic yoke. The magnetic yoke was oppositely poled so that a magnet which was moveable into the proximity of both permanent magnets outside the valve body constituted an actuating member that attracted one permanent magnet on the double-armed lever and repelled the other of the permanent magnets. European Publication EP0715109A1 also teaches a valve having a permanent magnet actuation mechanism.
All references cited herein are incorporated herein by reference in their entireties.